In such an arrangement, the dashboard, which is situated inside the vehicle and below the windshield, comprises a dashboard body that has a back face carrying an airbag module, which module comprises an enclosure containing the airbag and inflation means for inflating said airbag, and facing the corresponding opening in the dashboard body.
The opening, which is generally rectangular, is closed by one or two flaps, each of which has an edge that is hinged to a corresponding transverse edge of said opening. A firing channel, forming a spacer, is interposed between the airbag module and the back face of the dashboard body.
The front face of each flap and the front face of the dashboard body constitute a substantially continuous convex surface. Said convex surface may be covered by a skin, in order to make the flap substantially invisible to an occupant of the vehicle.
When an impact is detected, the airbag inflates automatically, so that it exerts pressure on the inside face of the flap, thereby causing it to open, against the covering that tears. That enables the airbag to be deployed through the dashboard towards the inside of the vehicle, in such a manner as to be interposed between an occupant of the vehicle and the dashboard.
The flap opens and the airbag is fully inflated within a lapse of time that must be sufficiently short to protect the occupant of the vehicle by preventing the occupant's head from hitting the dashboard or the windshield under the effect of the impact.
The airbag inflating thus causes the flap to open, also very rapidly, so that the free edge of said flap is actually stopped by the windshield that it generally hits, thereby causing the opening movement of the flap to cease.
In order to avoid destroying the windshield, provision is made, for example, for the flap to be flexible so as to absorb the energy from the impact so as not to break the windshield. The flap is thus less thick than the remainder of the dashboard, while also being hinged thereto.
In that context, the edge of the flap can be secured to the edge of the opening in the dashboard by an additional strip of plastics material injected into the thickness of the flap and into the thickness of the dashboard body. However, when the strip is injected hot, it is too flexible, and when it is injected cold, it is too fragile.
The hinge can thus be formed by a textile mesh overmolded on the inside face of the flap and on the inside face of the dashboard, but in practice the cohesion between the textile mesh and the inside faces is not sufficient in view of the magnitude of the forces involved during opening.
The hinge can also be in the form of a metal flap-reinforcement, a portion of which is fastened to the dashboard body. But there too, the bond between the metal reinforcement and the dashboard body is not sufficiently strong, and, in any event, the resulting assembly is of excessive weight.